Adjustment drive for a steering column, motor-adjustable steering column for a motor vehicle, and method for adjusting a bearing assembly of an adjustment drive

ABSTRACT

A motor adjustment drive for a vehicle steering column includes a threaded spindle with an axis. The threaded spindle engages a spindle nut. A drive unit and a gear wheel which is connected to the spindle nut or the threaded spindle for rotation therewith is driveable to rotate by the drive unit and is rotatably mounted in a bearing housing between two outer bearing rings that are axially supported at the bearing housing. The outer bearing rings each have, on their sides facing one another, a circumferential outer bearing face that is coaxial to the axis. Each outer bearing face lays opposite a bearing face embodied on the end side at the gear wheel. An outer bearing ring is axially resiliently supported at the bearing housing via an elastic element, which exerts an axial force that biases the two outer bearing rings toward each other.

PRIOR ART

The invention relates to an adjustment drive for a steering column thatis adjustable by motor for a motor vehicle, comprising a threadedspindle with an axis, said threaded spindle engaging in a spindle nut, adrive unit and a gear wheel which is connected to the spindle nut or thethreaded spindle for rotation therewith, which is driveable to rotateabout the axis by a drive unit and which is rotatably mounted about theaxis in a bearing housing in a bearing arrangement between two outerbearing rings that are axially supported at the bearing housing,

wherein the outer bearing rings each have, on their sides facing oneanother, a circumferential outer bearing face that is coaxial to theaxis, said outer bearing face in each case lying opposite a bearing faceembodied on the end side at the gear wheel. Furthermore, the inventionrelates to a steering column that is adjustable by motor for a motorvehicle, with such an adjustment drive and a method for setting abearing arrangement of an adjustment drive.

Steering columns for motor vehicles have a steering shaft with asteering spindle, at the rear end of which in the direction of travel,which faces the driver, a steering wheel is attached for introducing asteering command by the driver. The steering spindle is mounted in amanner rotatable about its longitudinal axis in an actuating unit, whichis held at the vehicle body by a carrying unit. There can be alongitudinal adjustment on account of the fact that the actuating unitis received in a casing unit connected to the carrying unit, which isalso referred to as guide box or box-section swinging fork, in atelescopically displaceable manner in the direction of the longitudinalaxis. A height adjustment can be realized by virtue of the actuatingunit or a casing unit receiving the latter being pivotably mounted atthe carrying unit. Adjusting the actuator unit in the longitudinal orheight direction allows an ergonomically comfortable steering wheelposition to be set relative to the driver position in an operatingposition, also referred to as a drive or actuating position, in whichthere can be a manual steering intervention.

For the purposes of adjusting the actuating unit relative to thecarrying unit, the prior art has disclosed the provision of amotor-driven adjustment drive with a drive unit that comprises anelectrical servomotor which is connected to a spindle drive—as a rule,via a transmission—that comprises a threaded spindle screwed into aspindle nut. By way of the drive unit, the threaded spindle and thespindle nut are driveable to rotate against one another about an axis,namely the threaded spindle axis, as a result of which the threadedspindle and the spindle nut can be moved in translational fashion to oneanother or away from one another, depending on the direction ofrotation. In one embodiment, the threaded spindle is driveable to rotateabout its threaded spindle axis by the drive unit which is fixedlyconnected to the actuating unit or the carrying unit and engages in thespindle nut which is fixedly attached in relation to a rotation aboutthe threaded spindle axis at the carrying unit or, alternatively, at theactuating unit. In the direction of the threaded spindle axis, thethreaded spindle is supported at the carrying unit or at the actuatingunit and the spindle nut is accordingly supported at the actuating unitor, alternatively, at the carrying unit such that a rotational drive ofthe threaded spindle brings about a translational adjustment of carryingunit and actuating unit relative to one another in the direction of thethreaded spindle axis. Therefore, this embodiment is also referred to asa rotational spindle drive.

In an alternative embodiment, the threaded spindle is coupled to thecarrying unit or, alternatively, to the actuating unit in anon-rotational manner with respect to rotation about its threadedspindle axis and the spindle nut is rotationally mounted accordingly atthe actuating unit or, alternatively, at the carrying unit but it isstationary in the direction of the threaded spindle axis. Like in thefirst embodiment, the threaded spindle is supported at the carrying unitor at the actuating unit in the direction of the threaded spindle axisand the spindle nut is accordingly supported at the actuating unit or atthe carrying unit such that the threaded spindle is displaceable in atranslational manner in the direction of the threaded spindle axis byvirtue of the spindle nut being driven to rotate by the drive unit. Thisembodiment is also referred to as a plunger spindle drive.

Like in the first-mentioned embodiment, a translational adjustment ofcarrying unit and actuating unit relative to one another is broughtabout in the direction of the threaded spindle axis as a result of therotational drive of the threaded spindle. In both embodiments, thespindle drive forms a motor-driven adjustment drive that is effectivebetween a carrying unit and an actuating unit, said adjustment drivefacilitating the adjustment of the actuating unit relative to thecarrying unit for adjustment purposes.

In order to realize a longitudinal adjustment of the actuating unit inthe direction of the longitudinal axis of the steering spindle, thespindle drive of an adjustment drive can be arranged between theactuating unit and a casing unit that receives the latter in an axiallylongitudinally displaceable manner, said casing unit also being referredto as a guide box or box-section swinging fork and being connected tothe carrying unit, wherein the threaded spindle axis can be alignedsubstantially parallel to the longitudinal axis. For the purposes of aheight adjustment, a spindle drive can be arranged between the carryingunit and an actuating unit that is mounted thereon so as to be pivotablein height or a casing unit, in which the actuating unit is received. Amotor-driven longitudinal and height adjustment can be embodied at asteering column individually or in combination.

The drive of the spindle drive is effected by the drive unit by way of agear wheel that is driveable to rotate about its axis, which isidentical to the threaded spindle axis, said gear wheel being connectedto the spindle nut or to the threaded spindle for rotation therewith,depending on the embodiment of the spindle drive. The gear wheel has atoothed portion in the form of a spur gear, with an outercircumferential toothing or worm toothing.

The gear wheel in each case has a circumferential bearing face that iscoaxial with the axis on each of its two end sides. In a bearingarrangement, the bearing faces are arranged between two correspondingouter bearing faces that are arranged on the sides of the two outerbearing rings facing one another, between which the gear wheel isrotatably mounted. As seen from the gear wheel, the outer bearing ringsare supported and affixed on the outside at the bearing housing in theaxial direction. As a result, holding and adjustment forces that act onthe gear wheel in both axial directions of the threaded spindle axis onthe spindle drive are transmitted via the gear wheel and the outerbearing rings onto the bearing housing, and are supported from there atthe actusting unit or the carrying unit.

Such an adjustment drive with a rotatably mounted and axially supportedgear wheel is known from U.S. Pat. No. 4,967,618, for example. Thebearing faces of the gear wheel have raceways for rolling bodies,specifically ball-bearing raceways of ball bearings. Ball bearings asrolling bodies are arranged between these ball-bearing raceways andthese opposing, corresponding ball-bearing raceways in the axially orobliquely opposing outer bearing faces of the outer bearing rings. As aresult, a bearing arrangement is formed, in which the gear wheel ismounted between two axial pressure bearings in a manner supported in theaxial direction, said pressure bearings in each case being formed by abearing face, an outer bearing face and the ball bearings arrangedtherebetween. The outer bearing rings are rigidly affixed to the bearinghousing.

During the assembly, a bearing arrangement is set by axially positioningand affixing the outer bearing rings relative to one another such thatthe ball bearings roll without play between the ball-bearing raceways.So that, where possible, no bearing play occurs during operation inorder to ensure low-noise running, the outer bearing rings are bracedagainst one another in the bearing housing such that the bearing facesand outer bearing faces are pressed against one another in the axialdirection. Here, on the one hand, the axial setting force exerted on theouter bearing rings must be high enough so that play-free running of theball bearings is ensured, even under temperature variations and in thecase of wear. However, on the other hand, the setting force must not betoo high, as this could result in an elevated breakaway torque of thegear wheel and increased wear.

In view of the problem explained above, it is an object of the presentinvention to specify an improved adjustment drive and a steering columnwith an improved adjustment drive, which has greater running smoothnessand less wear.

SUMMARY OF THE INVENTION

This object is achieved by an adjustment drive having the features ofclaim 1 and a steering column adjustable by motor for a motor vehiclehaving the features of claim 9. Claim 10 specifies a method for settinga bearing arrangement according to the invention of an adjustment drivefor a steering column that is adjustable by motor for a motor vehicle.Advantageous developments emerge from the dependent claims.

In order to achieve the aforementioned object, an adjustment drive for asteering column that is adjustable by motor for a motor vehicle havingthe features specified at the outset is proposed, in which, according tothe invention, at least one outer bearing ring is supported in anaxially resilient manner at the bearing housing by way of an elasticpreloading element, which exerts a preloading force that axially bracesthe two outer bearing rings against one another.

Unlike in the prior art, the two outer bearing rings are according tothe invention not rigidly supported at the bearing housing but areelastically clamped in the axis direction. The axis directioncorresponds to the direction of the longitudinal axis. The at least onepreloading element is formed by an axially effective spring element,which on its side that faces away from the bearing arrangement, i.e.,from the outer bearing rings, to the outside is supported axially at thebearing housing, and which on its other side acts axially on thecorresponding outer bearing ring. In the assembled operational state,the preloading element is preloaded or compressed so far in the axialdirection, i.e., in the direction of the longitudinal axis, that itexerts a predetermined preloading force on the outer bearing ring andsaid preloading element is affixed in this preloading or assemblyposition relative to the bearing housing. The preloading element, whichis axially loaded in this way, presses the outer bearing ring againstthe gear wheel with the elastic force, i.e., the spring force, as aresult of which said gear wheel is also pressed against the other outerbearing ring with the preloading force. Consequently, the bearingarrangement is elastically preloaded in the axis direction by way of thepreloading element.

An advantage of the invention is that the preloading force, which can beset during the assembly by compressing the preloading element, ensures amore uniform axial pressure between the bearing faces and thecorresponding outer bearing faces over the entire service life of theadjustment drive, even under inexpedient operating conditions, forexample thermal load or wear, as result of which an unwanted anddamaging bearing play is suppressed. In a rolling-element bearingarrangement, the rolling bodies roll without play and, in an alternativeplain bearing arrangement, an optimized sliding contact is ensured. Thisincreases the running smoothness and reduces wear.

It is possible that the preloading element exerts the preloading forceon the one of the two outer bearing rings, and the other outer bearingring is supported in an axially rigid manner at the bearing housing at acounter bearing. As a result thereof, the preloading force is axiallycoupled, in the preloading direction, into the bearing arrangement thatis stationary relative to the bearing housing. Alternatively, theprovision of two preloading elements, which, from both sides,respectively act on the outer bearing rings, is possible. As a resultthereof, the bearing arrangement is likewise elastically preloaded and,moreover, elastically held in both axis directions relative to thebearing housing. As a result, it is possible to elastically absorb anddampen torque peaks.

The preloading element can comprise a ring-shaped spring element. Thespring element can be elastically compressed axially by the preloadingforce and it permanently transfers said preloading force onto thebearing arrangement as the spring force. The ring-shaped embodiment thatis coaxial with the axis corresponds to the dimensions of the outerring, against which the spring element lies directly or indirectly inthe assembled state. The spring travel in the axial direction can beadapted to the deviations, expected during operation, as a result ofwear and temperature variations, and so these deviations that occurduring the service life are effectively compensated thanks to thesolution according to the invention. By way of example, the springelement can comprise a spring ring or wave ring, a coil spring, diskspring or leaf spring or the like, preferably made of spring steel, oralternatively, or else in combination, an elastomeric ring, rubber ringor O-ring that is likewise elastically deformable in the axial directionor a cord ring formed from an elastomer. Different constructions ofspring elements can be combined for the purposes of optimized spring anddamping properties, for example a spring ring and an O-ring at one orboth outer bearing rings.

The preloading element can comprise a securing element. This securingelement can be elastically compressed in the axial direction by thepreloading force and it permanently transfers said preloading force ontothe bearing arrangement as the spring force. The securing elementfurthermore serves as a holding or supporting element, which is securedat the bearing housing in the axial direction, for example by way of aninterlocking, force-fit and/or substance-to-substance connection. Theconnection can have a detachable embodiment, for example by way of aclamped, latched or screwed connection, or else it can benon-detachable, for example as a result of welding.

Preferably, the preloading element is embodied as an integral securingelement.

The securing element is preferably embodied as an integral sheet metalshaped part, preferably as a one-piece integral component. Preferably,the securing element is embodied in integral fashion as a springelement, wherein an intermediate element as a damping element isarranged between the spring element and the outer ring. By way ofexample, this intermediate element can be embodied as an elastomericelement, such as an O-ring, for example. Alternatively, the intermediateelement can be applied to the securing element, for example by way of acured-on elastomeric element.

In a preferred embodiment, provision can be made for the preloadingelement to be supported at a securing element that is connected to thebearing housing. The securing element serves as a holding or supportingelement, which is secured at the bearing housing in the axial direction,for example by way of an interlocking, force-fit and/orsubstance-to-substance connection. The connection can have a detachableembodiment, for example by way of a clamped, screwed or latchedconnection, or else it can be non-detachable, for example as a result ofwelding. A preloading element according to the invention can beelastically clamped between the securing element and an outer bearingring. Likewise, it is possible that one of the outer bearing rings issupported at the bearing housing via a securing element without aninterposed preloading element, said bearing housing then forming a rigidcounter bearing.

In terms of form and dimensions, the preloading element can be matchedto an outer bearing ring and a securing element, which may be embodiedas a ring-shaped or segment-shaped securing ring, for example. It ispossible to provide a securing element on an end side of a bearingarrangement which, on its other side, is supported against a counterbearing that is connected to, or formed at, the bearing housing.Likewise, it is possible that the bearing arrangement is secured betweentwo securing elements at the bearing housing such that the preloadingforce that is produced by the preloading element is introduced into thebearing housing via the securing elements.

In a development, provision can be made for the preloading element to beformed, at least in part, by the securing element. This can be achievedby virtue of the securing element per se having an elastic embodiment inthe axial direction. As a result, it receives a dual function,specifically, firstly, that of providing the support and hold at thebearing housing and, secondly, that of producing the elastic preloadingforce. By way of example, the securing element can be embodied as asecuring ring, made of spring steel, for example, which has a fasteningmeans, for instance holding rims or holding edges engaging in aninterlocking fashion, at its circumference. Away from the fasteningmeans, axially effective spring elements can be provided at the securingring, for example a conical portion of a disk spring, a wavy portion ofa wave spring, resilient logs or the like. The spring elements can besupported directly or indirectly at an outer bearing ring from theoutside.

Rolling bodies can be arranged between the gear wheel and the outerbearing rings. Here, the gear wheel in each case forms anangular-contact rolling-element bearing together with an outer bearingring and the rolling bodies arranged therebetween. Both an X-arrangementand an O-arrangement of the angular-contact rolling-element bearing canbe provided. Alternatively, an axial rolling-element bearing may also beprovided. Alternatively, it is also conceivable and possible for anouter bearing face and a corresponding bearing face to have slidingfaces that slide on one another for the purposes of forming anangular-contact plain bearing.

One of the two outer bearing rings can be supported at the bearinghousing at a counter bearing in an axially rigid manner. As a result,the bearing arrangement that is elastically loaded via the other outerbearing ring by the preloading element is supported in stationaryfashion at the bearing housing. The counter bearing can be fixedlyembodied on the bearing housing, or else it can be formed by a securingelement that is fastened to the bearing housing. The counter bearing canbe preferably embodied as a shoulder, wherein this shoulder ispreferably embodied by a shaping operation, for example bycircumferential rolling, wherein a bead formed on the outer lateral faceforms a shoulder on the inner lateral face. Alternatively, projectionsdistributed over the circumference can also form such a shoulder. By wayof example, these projections can be introduced into the bearing housingfrom the outside by way of local plastic deformations.

An advantageous embodiment of the invention provides for the bearinghousing to comprise a hollow cylindrical receiving space, in which theouter bearing rings and the gear wheel are arranged coaxially inrelation to the axis. The receiving space forms a passage with acircular inner cross section, in which the bearing arrangement, formedby the gear wheel and the outer bearing rings, is received in a coaxialfashion. Preferably, the securing element or elements likewise can beembodied in the ring-shaped manner as securing rings, which are arrangedand affixed in coaxial fashion in the receiving space.

A development provides for the securing element to comprise fasteningmeans for affixment inside the receiving space. As a result of thesecuring element being fastened to the inner wall in force-fit and/orinterlocking fashion, the entire bearing arrangement, including theaxial support, can be arranged in the bearing housing, resulting in acompact and protected structure being realizable. In an advantageousembodiment, the securing element is embodied as a securing ring with anouter cross section that corresponds to the inner cross section of thereceiving space of the bearing housing. Fastening means for connectionwith the inner wall of the receiving space can be arranged or formed atthe outer circumference of the preferably round securing ring. By way ofexample, the fastening means can comprise holding structures on theouter circumference of the securing ring, for example blade-shaped,sharp-edged edges or blades which can be introduced or pressed into theinner wall in an interlocking manner and which secure the securing ringagainst axial movements in order to axially affix a preloading elementor an outer bearing ring in the demanded preloaded position in thebearing housing.

Here, provision can be made for the fastening means to be embodied in aself-affixing manner. By way of example, this can be achieved by holdingstructures with the barb-like embodiment, which slide along the innerwall of the receiving space when the securing element is introducedaxially into the passage of the bearing housing in the preloadingdirection during the assembly and pressed with the preloading forceagainst the preloading element. In the operational state after theassembly, the securing element is axially loaded by the preloading forceagainst the preloading direction, as a result of which the barb-likeholding structures of the fastening means are radially spread apart andindependently cling on the inner wall, as a result of which the securingring is axially affixed relative to the bearing housing. By way ofexample, a cutting edge that is inclined relative to the axis can beprovided as a self-affixing fastening means, said cutting edge beingembodied or arranged at least in portions at the outer circumference ofthe securing ring. For assembly purposes, this facilitates the simpleaxial insertion in the preloading direction into the receiving spaceagainst the preloading element. After the assembly, the cutting edge isplastically buried into the inner wall radially by the preloading forceacting counter to the insertion direction and, as a result, it isaffixed in the axial direction in interlocking fashion. Suchself-affixing holding means with barb-like holding structures arerealizable with little outlay, facilitate a simple assembly andfacilitate secure hold.

The invention further comprises a steering column that is adjustable bymotor for a motor vehicle which comprises an adjustment drive with thefeatures described above, comprising a carrying unit, which isattachable to a vehicle body, and which holds an actuating unit, inwhich a steering spindle is rotatably mounted about a longitudinal axis,and comprising an adjustment drive, which is connected to the carryingunit and to the actuating unit, and by means of which the actuating unitis adjustable relative to the carrying unit, wherein the adjustmentdrive comprises a threaded spindle with an axis, said threaded spindleengaging in a spindle nut, a drive unit and a gear wheel which isconnected to the spindle nut or the threaded spindle for rotationtherewith, which is driveable to rotate about the axis by the drive unitand which is rotatably mounted about the axis in a bearing housing in abearing arrangement between two outer bearing rings that are axiallysupported at the bearing housing, wherein the outer bearing rings eachhave, on their sides facing one another, a circumferential outer bearingface that is coaxial to the axis, said outer bearing face in each caselying opposite a bearing face embodied on the end side at the gearwheel.

As a result, it is possible to achieve an improved running smoothness ofthe adjustment drive under all occurring operating conditions of asteering column, which is of particular importance for the acceptance bythe driver. Furthermore, the wear, and hence the servicing outlay, isadvantageously reduced.

A method according to the invention for setting a bearing arrangement ofan adjustment drive for a steering column that is adjustable by motorfor a motor vehicle, comprising a threaded spindle with an axis, saidthreaded spindle engaging in a spindle nut, and a gear wheel which isconnected to the spindle nut or the threaded spindle for rotationtherewith and which is rotatably mounted about the axis in a bearinghousing in a bearing arrangement between two outer bearing rings thatare axially supported at the bearing housing, wherein an outer bearingring is supported in an axially resilient manner at the bearing housingby way of an elastic preloading element, comprises the steps of:

A) applying an axial preloading force to the preloading element,

B) applying a load moment to the gear wheel and measuring the loadmoment,

C) measuring a bearing state variable (load moment itself or else:displacement of the gear wheel) that is correlated with the load moment,

D) comparing the measured bearing state variable with a predeterminedstate target value,

E) should the measured bearing state variable deviate from the statetarget value (within predetermined tolerance ranges): modifying theaxial preloading force,

E) should the measured bearing state variable attain the state targetvalue (within predetermined tolerance ranges): affixing the preloadingelement (9) in an axial preloading position at the bearing housing andcompleting the setting process.

The method according to the invention facilitates optimized setting of abearing arrangement having the above-described features, which comprisesa preloading element according to the invention. Here, at least onebearing state variable, which depends directly or indirectly on thepreloading force, is brought within predetermined tolerances to a statetarget value, i.e., adjusted into an ideal state target range. As aresult, it is possible to obtain high running smoothness, low wear and astiffness of the bearing arrangement that is as high as possible.

Applying an axial preloading force onto the preloading element cancorrespond to applying an axial pressing-in force that acts on thepreloading element, wherein the acting pressing-in force is counter tothe preloading force.

In the first step A), a pre-assembled bearing arrangement is provided,wherein the outer bearing rings and the at least one preloading elementare held together with a defined, predetermined start value of thepreloading force. Here, the start value is selected in such a way thatthe preloading force lies at, or below, a threshold required for theoperationally ready assembly such that, expressed differently, the axialpreloading force produces a loose pre-assembly.

In the next step B), a load moment is exerted onto the gear wheel. Byway of example, a load torque can be a breakaway torque, with which thegear wheel has to be driven to rotate about its axis in order to carryout a rotation in the bearing arrangement, or else a tilt ordisplacement moment, that acts transversely to the axis on the gearwheel. These two operating cases are explained in more detail below.

Subsequently, in step C), a bearing state variable that is correlatedwith the load moment is measured. Here, it is possible to measure thesize of the load moment itself, for example the breakaway torque or tiltmoment coupled into the gear wheel, and, as an alternative or inaddition thereto, it is also possible to measure a variable that dependson the load moment, such as a displacement of the gearwheel, forexample, a tilt in relation to the axis, which is produced by an inputcoupled load moment, for example an aforementioned tilt moment.

In step D), the measured bearing state variable is compared to apredetermined state target value. The state target value defines areference value that corresponds to a bearing state that should beobserved during the operational state.

Step E) is carried out should the measured bearing state variabledeviate from the state target value—within predetermined toleranceranges. To this end, the axial preloading force is modified in order tomove the actual value of the bearing state variable in the direction ofthe state target value. If the measured bearing state variable reachesthe state target value—within predetermined tolerance ranges—, thepreloading element is affixed, i.e., supported, in axial preloadingposition at the bearing housing such that it permanently exerts the setpreloading force onto the bearing arrangement. With this, the settingprocess is complete.

Preferably, the preloading force is exerted on a securing element thatis arranged in front of an outer bearing ring. The securing element ismoved axially against the outer bearing ring, and pressed thereagainst,in the direction of the preloading force. As the securing element ismoved further against the preloading element, the compression thereof isincreased, and the preloading force is correspondingly increased. Oncethe value of the preloading force that was predetermined during thesetting process is reached, the securing element is affixed to thebearing housing in the preloading position set in that case.

An advantage of the method according to the invention is that thebearing arrangement can be preloaded in a closed-loop control process,taking account of a bearing state variable that depends on thepreloading force.

A possible embodiment of the method comprises the steps of:

B1) applying a breakaway torque as load moment for rotational driving ofthe gear wheel and measuring the breakaway torque in the process as acorrelating bearing state variable,

C1) comparing the measured breakaway torque with a predetermined torquetarget value as a bearing state variable,

E1) should the measured breakaway torque as a bearing state variable besmaller than the predetermined torque target value as a state targetvalue: increasing the axial preloading force,

F1) should the breakaway torque as a bearing state variable attain thepredetermined torque target value as a state target value: affixing thepreloading element in an axial preloading position at the bearinghousing and completing the setting process.

Consequently, in this embodiment of the method, the breakaway torquecorresponds to the load moment, the measured breakaway torquecorresponds to the correlated bearing state variable and the torquetarget value corresponds to the state target value.

In order to carry out the setting, the bearing arrangement comprisingthe outer bearing rings and the gear wheel, and optionally the rollingbodies arranged therebetween, is arranged in the bearing housing. Thegear wheel is driven to rotate. The drive can be implemented by thedrive unit of the adjustment drive. Alternatively, in the case of arotational spindle drive, in which the threaded spindle is connected tothe gear wheel for rotation therewith, the drive of the gear wheel canbe brought about by an external adjustment drive, which drives thethreaded spindle to rotate.

Here, the load moment is the breakaway torque, i.e., the drive momentthat has to be applied to rotate the gear wheel in the bearingarrangement. This drive moment can be measured by means of suitablesensors, for example by way of torque sensors, or by way of a motorcurrent of the drive unit or an external adjustment drive.

An axial preloading force is applied to the preloading element duringthe rotating drive, for example by way of a securing element thataxially presses the preloading element against an outer bearing ring.Here, the preloading force is preferably measured by means of suitableforce sensors.

Subsequently, the preloading force is increased step-by-step orcontinuously. As a result, there is an increase in the bearing frictionof the bearing arrangement, and the measured breakaway torque, whichcorrelates to the preloading force, likewise increases.

The currently measured breakaway torque, which correlates to an appliedpreloading force, is compared, either step-by-step or continuously,preferably in an automated manner, to a predetermined torque targetvalue.

If the measured breakaway torque is less than the predetermined torquetarget value, this means that the bearing play is still too large, orthe preload is still too small, and so the required rigidity of thebearing arrangement and play-free running under load conditions duringoperation are not yet ensured. In this case, the preloading force isincreased, and the measured breakaway torque is measured again andcompared to the torque target value.

The aforementioned steps are run through until the breakaway torqueattains the predetermined torque target value. In the axial positionattained in the process, the preloading position, the preloading elementis affixed relative to the bearing housing, preferably by a securingelement. In the preloading position, the preloading element is supportedaxially at the bearing housing in such a way in the process that itpermanently exerts the set preloading force on the outer bearing ring.

As a result of this, force-controlled or torque-controlled setting ofthe breakaway torque is realized, wherein the preloading force isregulated by the measured breakaway torque. Automated, precise settingof the breakaway torque is facilitated. The preloading element ensuresthat the set breakaway torque of the adjustment drive remainssubstantially constant over the entire service life of the adjustmentdrive, independently of wear and operating conditions.

As an alternative to, or else in addition or together with, theabove-described embodiment, the method according to the invention canprovide the following steps:

B2) applying a tilting moment as a load moment across the axis on thegear wheel and measuring a displacement of the gear wheel relative tothe bearing housing in the process as a correlating bearing statevariable,

C2) comparing the measured displacement as a bearing state variable witha predetermined stiffness threshold as a state target value,

E2) should the measured displacement as a bearing state variable begreater than a predetermined stiffness threshold as a state targetvalue: increasing the axial preloading force,

F2) should the measured displacement as a bearing state variable attainthe predetermined stiffness threshold: affixing the preloading elementin an axial preloading position at the bearing housing and completingthe setting process.

Consequently, in this embodiment of the method, the tilt momentcorresponds to the load moment, the measured displacement of the gearwheel relative to the bearing housing corresponds to the correlatedbearing state variable and the stiffness threshold corresponds to thestate target value.

By applying a tilt moment, the bearing arrangement is subjected tobending in the transverse direction. The lateral deformation occurringin the process is a measure for the stiffness of the bearingarrangement. The stiffness of the bearing arrangement depends on thepreloading force, with a high preloading force correlating with a highstiffness.

Like in the above-described embodiments, a start value of the preloadingforce is initially set. A tilting moment is exerted on the gear wheel asa load moment.

By way of example, the tilt moment can be input coupled by a tilting orbending force that is introduced transversely into the threaded spindle.

The displacement of the gear wheel produced by the tilt moment ismeasured, for example by way of a radial deflection of the threadedspindle connected to the gear wheel.

The measured displacement is compared to a stiffness threshold. Thelatter denotes a reference value of the displacement that is correlatedto the necessary stiffness.

The required stiffness is not provided for as long as the measureddisplacement is greater than a predetermined stiffness threshold. Inthis case, the preloading force is increased until the measureddisplacement is less than or equal to the stiffness threshold withinpredetermined tolerance ranges. This realizes travel-controlled settingof the stiffness, wherein the preloading force is regulated by themeasured displacement of the gear wheel.

As described above, the preloading force can be set depending on thebreakaway torque or tilt moment, or else on the breakaway torque andtilt moment. This allows optimized setting of an adjustment drive, whichensures a stiffness that is as high as possible with an easyadjustability.

The preloading force can be measured when the preloading force isapplied. Faults can be detected by comparison with the other measurementvariables. By way of example, a deviatingly high breakaway torque in thecase of a relatively small preloading force can indicate a defect thatcan lead to a stiff bearing.

The breakaway torque and/or the tilt moment can be introduced by way ofthe threaded spindle. The threaded spindle, which is securely connectedto the gearwheel in the case of a rotational spindle drive inparticular, can be driveable to rotate with an external adjustment drivein order to drive the gearwheel to rotate. As a result of a tilt forcebeing introduced across the axis into the threaded spindle at an axialdistance, a tilt moment can be introduced into the gear wheel, both inthe case of a plunger spindle drive and in the case of a rotationalspindle drive.

Furthermore, the invention relates to a further method for setting abearing arrangement of an adjustment drive for a steering column that isadjustable by motor for a motor vehicle, comprising a threaded spindlewith an axis, said threaded spindle engaging in a spindle nut, and agear wheel which is connected to the spindle nut or the threaded spindlefor rotation therewith and which is rotatably mounted about the axis ina bearing housing in a bearing arrangement between two outer bearingrings that are axially supported at the bearing housing, wherein anouter bearing ring (93) is supported in an axially resilient manner atthe bearing housing by way of an elastic preloading element, comprisingthe steps of:

A) applying an axial preloading force to the preloading element,

B) measuring the axial preloading force,

D) comparing the measured preloading force with a predetermined targetpreloading force,

E) should the measured preloading force deviate from the predeterminedtarget preloading force: modifying the axial preloading force,

F) should the measured preloading force attain the predetermined targetpreloading force: affixing the preloading element in an axial preloadingposition at the bearing housing and completing the setting process.

Preferably, the target preloading force can comprise a range.Consequently, the target preloading force is embodied as a targetpreloading range. This range can be established in trials such that thebearing arrangement satisfies the respective requirements in respect ofrunning smoothness, stiffness and breakaway torque in this range.

The preloading force can be exerted on a securing element that isarranged in front of an outer bearing ring. Here, it is advantageous ifthe securing element is movable relative to the bearing housing in thedirection of the preloading force and embodied to affix itself at thebearing housing against the preloading force. As described above, theouter bearing rings and the gear wheel can be arranged coaxially in ahollow cylindrical receiving space of the bearing housing and thesecuring element is formed by a securing ring, which has barb-likefastening means. Such a self-affixing securing ring can easily bepressed against the bearing arrangement in the preloading directionunder the effect of the preloading force. In the assembled state, thepreloading force now acting as a result of the spring force of thepreloading element acts in the opposite direction on the securing ring,as a result of which the latter clings on or buries itself in thebearing housing in an interlocking manner by way of appropriate cuttingedges, and affixes itself independently in its preloading position.

Preferably, the core element lies outside of the power flow between thebearing rings. As a result, a force acting on the bearing rings in thedirection of the axis is not introduced into the core element. Thebearing rings that support one another form a support device whichsupports pressure forces acting on the bearing rings outside of the coreelement and consequently keeps these away from the core element.

Furthermore, an adjustment drive for a steering column that isadjustable by motor for a motor vehicle is proposed for achieving theobject, said adjustment drive comprising a threaded spindle with anaxis, said threaded spindle engaging in a spindle nut, a drive unit anda gear wheel which is driveable to rotate about the axis by the driveunit and which has a toothing portion, which is arranged axially betweentwo circumferential bearing faces that are coaxial with the axis,wherein the gear wheel is connected to the spindle nut or the threadedspindle for rotation therewith. According to the invention, what isproposed for a generic adjustment drive with the aforementioned featuresis that the gear wheel has a core element, two bearing rings beingconnected therewith, said bearing rings each having a bearing face andsupporting one another axially.

Preferably, the core element lies outside of the power flow between thebearing rings. As a result, a force acting on the bearing rings in thedirection of the axis is not introduced into the core element. Thebearing rings that support one another form a support device whichsupports pressure forces acting on the bearing rings outside of the coreelement and consequently keeps these away from the core element.

In the gear wheel according to the invention, the bearing rings areconnected to a core element at the end side, and so an easy-to-assembleintegral component is provided.

Axially, the bearing rings are applied on both sides of the toothingportion and each have a respective bearing face on their outer sides,which face away from the core element and which also form outer sides ofthe gear wheel. Here, according to the invention, the bearing rings areconnected to one another in such a way that a force that is introducedonto the bearing faces in the axial direction is transferred from theone bearing ring to the other bearing ring without the core elementbeing loaded by the force between the bearing rings. Expresseddifferently, the core element is kept with little load between thebearing rings in the axis direction when an axial force is introduced,for example when applying an axial loading force for setting thebearings without play. Here, the axial power flow between the bearingrings can be established by virtue of the two bearing rings contactingone another and directly supporting one another axially, or it can beestablished indirectly, wherein a force transmission element may bearranged between the two bearing rings, said force transmission elementlikewise not transmitting any force onto the core element in the axialdirection. In any case, the force transmission in the axial direction iseffected, without interposing the core element, via the stiff structurefor force transmission or conduction that is formed by the bearingrings, independently of the core element. The two bearing rings can alsobe embodied as a one-piece integral component.

The bearing faces are arranged between outer bearing faces of a bearingarrangement. In each case, one outer bearing face, which is usuallyarranged at an outer ring, lies axially opposite a bearing face in thiscase such that the bearing gap is situated between the outer bearingface and bearing face. As a result of the outer bearing faces beingadjusted relative to one another axially, it is possible to set thedistance to the bearing faces, and hence the bearing play, and it ispossible to apply an axial force in order to brace the bearing facesbetween the outer bearing faces without play.

The axial forces acting on the bearing rings are transferred in an axialforce flow past the core element by way of the mutual support accordingto the invention. A load exerted axially onto the bearing faces isabsorbed by the structure according to the invention between the bearingrings and thereby kept away from the core element. As a result of nomaterial of the core element being situated in the axial force flow, itis not loaded by the forces occurring when the bearing is braced and bythe forces occurring during operation.

As a result, the possibility of independently optimizing the materialsof the bearing rings and of the core element in view of the propertiesrequired during operation arises. Preferably, the bearing rings canconsist of a hard material that does not yield to pressure, whichfacilitates a rigid and loadable axial connection, said connection beingsuitable for receiving the forces acting on the bearing face, andpreferably facilitates an integrated embodiment of plain bearing facesor rolling body raceways. By way of example, steel fulfils theserequirements well. By contrast, the core material can consist of asofter material, for example of softer metal alloys, such as brass, forexample, or plastics. Plastics, in particular, can be optimized in viewof their properties to the respective requirements, for example inrespect of elasticity and sliding properties for realizing drives andspindle drives with little play and smooth running. The property of suchplastics materials to flow under pressure and to plastically deform isnot decisive in the design according to the invention of a gear wheelbecause potentially damaging forces are received by the bearing ringsthat are supporting one another and hence an unwanted deformation of thecore element arranged between the bearing rings in the axial directionis practically excluded. As a result, a greater design freedom than inthe prior art is facilitated in view of the combination of differentmaterials for the bearing rings and the core element.

The bearing rings can be connected fixedly, preferably non-detachably,to the core element, for example by substance-to-substance bonding suchas welding or adhesive bonding, or by embedding or insert moulding. As aresult, the gear wheel can be provided as an integral, easy-to-assemblecomponent.

The bearing rings are preferably attached to both axial end sides of thecore element, wherein the bearing faces, as seen from the core element,are directed axially to the outside, for example as substantiallycircular-ring-shaped or conical bearing faces. In one bearingarrangement, the bearing faces are in sliding contact, or by ways ofrolling bodies in rolling-body contact, with corresponding outer bearingfaces that are arranged axially on both sides of the gear wheel. Here,it is possible to realize angular-contact bearings by conical bearingfaces, which may also be provided with rolling body raceways that are atan angle to the axis, said angular-contact bearings simultaneouslyfacilitating an optimized radial and axial bearing and support.

Initially, the bearing rings can be provided as two separate components,which are assembled in the gear wheel with the core element such thatthey are connected to one another directly or indirectly in the axialdirection for axial force transmission purposes. The force transmissioncan be effected in direct contact, or by way of force transmissionelements disposed therebetween, although these do not introduce anyforce into the core element in the axial direction.

Provision can be made for the two bearing rings to be embodied togetherin integral fashion. Here, both bearing rings are embodied at aone-piece integral bearing ring element. By way of example, such abearing ring element can have a sleeve-shaped or drum-shaped embodiment,with the bearing faces being situated in the region of the axial endsides. In the axial direction, the bearing faces are continuouslyconnected to one another in integral fashion by way of the bearing ringelement. The power flow in the case of an axial load is consequentlyeffected through the continuous material of the bearing ring element. Itis likewise conceivable and possible to initially manufacture separatebearing rings and to connect these to one another to form a bearing ringelement in a further step, before the connection to the core element iseffected.

The gear wheel can be mounted in rolling-element bearings, wherein thebearing faces of the bearing rings have rolling body raceways,preferably ball-bearing raceways. The axially opposing outer bearingfaces that are assigned to the bearing rings likewise have correspondingball-bearing raceways, and ball bearings as rolling bodies are arrangedso as to be able to roll between the ball-bearing raceways. In thisembodiment, the bearing rings form inner rings of rolling-elementbearings, preferably with bearing faces or ball-bearing raceways lyingat an angle to the axis such that angular-contact ball bearings areformed, which facilitate the reception of bearing loads in the axial andradial direction in the case of the compact design. Preferably, thebearing faces are embodied in such a way that the gear wheel is mountedin the housing by means of an X-bearing.

The bearing rings and the outer bearing faces can also have slidingfaces that slide on one another such that a plain bearing arrangement isformed.

It is possible that the bearing rings are embodied as sheet metal shapedparts, preferably from sheet steel. Such sheet metal shaped parts can bemanufactured efficiently as press/punch parts with the demandedproperties. Individual bearing rings can be made available as bushings,which each have a bearing face and which, according to the invention,are connected to one another and to the core element. Both bearing ringsalso can be arranged at a single bearing ring element, which can beproduced by connecting two bearing rings or which can be manufactured asan integral sheet metal shaped part from a single sheet metal portion.The sheet metal shaped part can have integrally formed raceways forrolling bodies, preferably ball-bearing raceways, that can be embodiedto be sufficiently hard, for example also by means of continuous orpartial hardening or hard coating. The raceways are connected byintegrally continuous sheet metal portions.

Alternatively, it is likewise conceivable and possible for the bearingrings to be embodied as a cold extrusion part or as a selective lasermelting component.

An advantageous embodiment provides for the toothing portion and/or thespindle nut and/or a connecting piece to have an integral one-pieceembodiment with the core element. The core element can be manufacturedfrom materials which, on account of their material properties, are wellsuited to the use as gear elements. By way of example, plastics are wellsuited for providing smooth running and low-wear toothings and screwdrives. According to the invention, the toothing can be moulded into thecore element consisting of plastics for the drive engagement with thedrive unit and—in the case of a plunger spindle drive with a spindle nutthat is driveable to rotate—the female thread of the spindle nut can bemoulded into the core element consisting of plastics. In the case of arotation spindle drive, the core element likewise can comprise atoothing that is integrally moulded into plastics, and a connectingpiece for connecting the gear wheel to the threaded spindle for rotationtherewith.

It is advantageous for the core element to be embodied as a plasticsinjection moulded part. Manufacturing by way of the injection mouldingmethod from thermoplastic plastics, for example polypropylene (PP),polyoxymethylene (POM) or the like, is efficient and facilitatesflexible shaping, also in view of the embodiment of the toothing or thefemale thread. Optionally, the plastics can be provided with areinforcement, for example by the addition of reinforcement fibres, inorder to increase the strength,

Manufacturing the core element as a plastics injection moulding partfacilitates a particularly advantageous connection to the bearing ringsby virtue of the core element being moulded onto the bearing rings.Here, the bearing rings are arranged in the cavity of an injectionmoulding tool and at least partly surrounded by the molten liquidplastics injected therein such that, after cooling, they aresubstance-to-substance bonded to the plastics of the core element. Aparticularly secure connection can be reached by virtue of the bearingrings having interlock elements that are substance-to-substance bondedand connected in an interlocking fashion to the core element. By way ofexample, the interlock elements can have perforations and/or projectionsand/or a knurling of the bearing ring or rings, which are penetrated bythe plastics material, and embedded in the latter, when injectionmoulding the core element. After cooling, this results in the bearingrings, or a bearing ring element comprising both bearing rings, beinganchored in a non-detachably secured manner by an interlockingconnection and substance-to-substance bond in the core element by way ofthe interlock elements. As a result, the toothing, the female threadand/or a connecting piece can be connected to the bearing rings securelyand positionally accurately in the long-term. Even in the case of a coreelement that is not manufactured as an injection moulded part, theinterlock elements can serve to produce an interlocking connectionbetween the core element and one or both bearing rings.

In an adjustment drive according to the invention, the bearing rings canbe braced between corresponding outer bearing rings of a bearingarrangement. Between the outer bearing rings, the gear wheel isrotatably mounted by way of the bearing faces of the bearing rings. Inorder to set and minimize the bearing play, the outer bearing rings canbe moved against one another, and hence against the respectivelycorresponding bearing rings, in the axial direction and can be pressedon with a preloading force. The preloading force can be produced byelastic preloading elements, which are supported at a secure counterbearing, for example a bearing housing in the axial direction. Dependingon the embodiment of the steering column, the counter bearing can besecurely attached in the axial direction to the actuating unit, thecarrying unit or a casing unit connected to the carrying unit. Such apreloading element can comprise a spring element, for example a discspring or wave spring, or else an elastomeric element in the form of arubber ring or the like.

DESCRIPTION OF THE DRAWINGS

Below, advantageous embodiments of the invention are described in moredetail on the basis of the drawings. In detail:

FIG. 1 shows a schematic perspective view of a steering column accordingto the invention,

FIG. 2 shows a further perspective view of the steering column accordingto the invention as per FIG. 1, from a different viewing angle,

FIG. 3 shows a longitudinal section along the threaded spindle axisthrough an adjustment device of a steering column as per FIGS. 1 and 2in a perspective view,

FIG. 4 shows a longitudinal section as in FIG. 3 in a side view,

FIG. 5 shows a pulled-apart illustration of the spindle drive as perFIGS. 3 and 4,

FIG. 6 shows a longitudinal section through the bearing arrangement of aspindle drive as in FIG. 4 when setting the bearing arrangement,

FIG. 7 shows a second embodiment of an adjustment device in a view as inFIG. 4,

FIG. 8 shows a third embodiment of an adjustment device in a view as inFIG. 4,

FIG. 9 shows a fourth embodiment of an adjustment device in a view as inFIG. 4,

FIG. 10 shows a fifth embodiment of an adjustment device in a view as inFIG. 4.

EMBODIMENTS OF THE INVENTION

In the various figures, the same parts are always provided with the samedesignations, and are therefore in each case also generally onlyreferred to or mentioned once.

FIG. 1 shows, from obliquely top right, a steering column 1 according tothe invention in a schematic perspective view of the rear end inrelation to the direction of travel of a vehicle (not illustrated here),where the steering wheel (not illustrated here) is held in the operatingregion. FIG. 2 shows a steering column 1 in a view from the oppositeside, i.e., as seen from top right.

The steering column 1 comprising a carrying unit 2, which is embodied asa console that comprises fastening means 21 in the form of fasteningbores for attachment to a vehicle body (not illustrated here). Thecarrying unit 2 holds an actuating unit 3, which is received in a casingunit 4—which is also referred to as a guide box or box-section swingingfork.

The actuating unit 3 has a steering column tube 31, in which a steeringspindle 32 is mounted to be rotatable about a longitudinal axis L, saidsteering spindle extending axially in the longitudinal direction, i.e.,in the direction of the longitudinal axis L. Formed at the rear end ofthe steering spindle 32 is a fastening portion 33, a steering wheel (notillustrated here) being attachable thereon.

In order to realize a longitudinal adjustment, the actuating unit 3 isreceived in the casing unit 4 so as to be telescopically displaceable inthe direction of the longitudinal axis L in order to be able to positionthe steering wheel that is connected to the steering spindle 32 forwardand backward in the longitudinal direction relative to the carrying unit2, as indicated by the double-headed arrow parallel to the longitudinalaxis L.

The casing unit 4 is mounted in a pivot bearing 22 at the carrying unit2 in a manner to be pivotable about a horizontal pivot axis S that istransverse to the longitudinal axis L. In the rear region, the casingunit 4 is connected to the carrying unit 2 via an actuating lever 41. Asa result of a rotational movement of the actuating lever 41 by means ofan illustrated actuating drive 6 (see FIG. 2), the casing unit 4 can bepivoted relative to the carrying unit 2 about the pivot axis S that lieshorizontally in the installed state, as a result of which it is possibleto adjust a steering wheel, attached to the fastening portion 33, in theheight direction H, as indicated by the double-headed arrow.

A first adjustment drive 5 for adjusting the longitudinal position ofthe actuating unit 3 relative to the casing unit 4 in the direction ofthe longitudinal axis L comprises a spindle drive with a spindle nut 51with a female thread 74 extending along an axis G, a threaded spindle 52engaging therein; i.e., the male thread of said threaded spindle isscrewed into the corresponding female thread 74 of the spindle nut 51.The threaded spindle axis of the threaded spindle 52 is identical to theaxis G and extends substantially parallel to the longitudinal axis L.

The spindle nut 51 is mounted in a bearing housing 53 so as to berotatable about the axis G, said bearing housing being securelyconnected to the casing unit 4. In the direction of the axis G, thespindle nut 51 is axially supported at the casing unit 4 via the bearinghousing 53, as will still be explained in more detail below.

With a fastening element 54 embodied at the rear end thereof, thethreaded spindle 52 is connected to the actuating unit 3 via atransmission element 34, to be precise in a manner fixed in thedirection of the axis G or the longitudinal axis L and stationary inrespect of rotation about the axis G. As a result of the spindle nut 51that is driveable to rotate and the threaded spindle 52 that isstationary in respect of rotation, a so-called plunger spindle drive isrealized.

The transmission element 34 extends from the actuating unit 3 through aslot-shaped passage opening 42 in the casing unit 4. In order to adjustthe steering column 1 in the longitudinal direction, the transmissionelement 34 can be moved freely along in the passage opening 42 in thelongitudinal direction.

The adjustment drive 5 has an electric servomotor 55, by means of whichthe spindle nut 51 is driveable to rotate in respect of the axis Grelative to the stationary threaded spindle 52. As a result, it ispossible—depending on the direction of rotation of the servomotor 55—todisplace the threaded spindle 52 in the direction of the axis G intranslational fashion relative to the spindle nut 51 such that,accordingly, the actuating device 3 connected to the threaded spindle 52is adjusted in the direction of the longitudinal axis L relative to thecasing unit 4 connected to the spindle nut 51. The drive of the spindlenut 51 and the support of the spindle nut 51 in the direction of theaxis G at the casing unit 4 will still be explained in detail furtherdown.

In FIG. 2, which shows a perspective view of the steering column 1 fromthe side lying at the back in FIG. 1, it is possible to recognize how asecond adjustment drive 6 for adjusting the height direction H isattached to the steering column 1. This adjustment drive 6 comprises aspindle nut 61, in the female thread 74 of which a threaded spindle 62engages along an axis G. The threaded spindle 62 is mounted so as torotatable about the axis G in a bearing housing 63, which is fastened atthe casing unit 4, axially supported, in the direction of the axis G, atthe casing unit 4 and driveable, optionally in both directions ofrotation, by an electric servomotor 65 so as to be rotatable about theaxis G. This will still be explained in detail further down.

The spindle nut 61 is attached in a stationary manner in respect of arotation about the axis G at one end of the two-arm actuating lever 41,which is mounted at the carrying unit 22 so as to be are rotatable abouta pivot bearing 23, the other arm of said actuating lever beingconnected, with the other end thereof, to the casing unit 4.

By rotating the threaded spindle 61, it is possible—depending on thedirection of rotation of the servomotor 65—to displace the spindle nut61 in translational fashion relative to the threaded spindle 62 in thedirection of the axis G such that, accordingly, the casing unit 4, whichis connected to the spindle nut 41 via the actuating lever 41, togetherwith the adjusting device 3 received therein can be adjusted up or downin the height direction H relative to the carrying unit 2, as indicatedby the double-headed arrow. The drive of the threaded spindle 62 and thesupport of the threaded spindle 62 in the direction of the axis G at thecasing unit 4 will still be explained in detail below.

FIG. 3 and FIG. 4 present a longitudinal section through the bearinghousing 63 of the adjustment drive 6 along the axis G in differentviews.

A gear wheel 7 designed according to the invention is fastened to thethreaded spindle 62 for rotation therewith in respect of the axis G. Thegearwheel 7 has a core element 71 made out of plastics, which ispreferably produced from a thermoplastic such as PP, POM or the like asa plastics injection moulded part. At its outer circumference, thegearwheel 7 comprises at the core element 71 a circumferential toothing72 that is coaxial to the axis G, said toothing being embodied as a wormtoothing in the illustrated example such that the gearwheel 7 forms aworm wheel. A worm 66 that is driveable to rotate by the servomotor 65engages in the toothing 72.

In the region of a central connecting portion 73, which forms aconnecting piece, the core element 71 is connected to the threadedspindle 62 for rotation therewith. By way of example, the connection canbe embodied as a substance-to-substance bond by virtue of the coreelement 71 being moulded onto the threaded spindle 62 in the process ofinjection moulding to the threaded spindle 62. In addition or as analternative thereto, an interlocking and/or any other type of fasteningmay be provided.

Bearing rings 8 of the gear wheel 7 are fixedly connected to the coreelement 71. Each bearing ring 8 has a ring-shaped bearing face 81 thatis coaxial to the axis G and embodied as the ball-bearing raceway. Asseen from the core element 71, the two bearing faces 81 run to theoutside, in an end-side conical manner. Expressed differently, theball-bearing raceways are at an angle to the axis G.

Axially, the bearing rings 8 comprise support portions 82 that aredirected against one another in the direction of the axis G, saidsupport portions directly lying against one another in the shown examplesuch that the bearing rings 8 are directly supported against one anotherin the direction of the axis G. In particular, no plastics material ofthe core element 71 is situated between the support portions 82 of thebearing rings 8 that are in contact with one another.

The bearing rings 8 are preferably embodied as sheet metal shaped parts,particularly preferably as press/punch parts made of sheet steel. Forthe purposes of connection to the gear wheel 7, the plastics of the coreelement 71 is injection moulded onto the bearing rings 8 and the latteris thus embedded into the core material 71 in a substance-to-substancebonded and interlocking manner, apart from the bearing faces 81 that areexposed to the outside on the end side. Optionally, provision can bemade of a fixing element 83, at which the two bearing rings 8 arepositioned relative to one another and held during the insert mouldingwith plastics such that they lie against one another axially in thedirection of the axis G. However, the fixing element 83 can also beomitted. Alternatively, it is also conceivable to directly connect thebearing rings 8 prior to insert moulding, for example by point weldingor the like.

The bearing faces 81 from the inner rings of a rolling-element bearingarrangement 9, which comprises ball bearings 91 that are held in arotatable manner in a ball-bearing cage 92 and that are arranged so isto roll in the axial bearing gap between said ball-bearing raceways ofthe bearing faces 81 and corresponding ball-bearing raceways in outerbearing rings 93. As seen from the gear wheel 7, the outer bearing rings93 are supported axially to the outside on both end sides by way ofelastic spring elements 94, which form preloading elements, elastomericrubber rings in the shown example, against axial counter bearings in theform of securing rings 95, which in turn are connected in a mannerstationary in the axial direction of the axis G to the bearing housing53, for example by wedging, caulking or jamming. The spring element 94likewise can be embodied as a wave spring or disk spring.

In the embodiment illustrated in FIG. 4, spring elements 94 that areembodied as preloading elements are arranged in both end sides of thegear wheel 7, said spring elements being supported axially at thebearing housing 63 by the two securing rings 94 and being elasticallybraced axially. Here, the spring force acts as a preloading force F onthe bearing faces 81 via the outer bearing rings 93 and the ballbearings 91, and so the gearwheel 7 is preloaded between the rollingelement bearing arrangements 9 axially.

For affixing purposes, the securing rings 95 can have at their outercircumference fastening means 951, for example partly or completelycircumferential cutting edges that protrude to the outside and that burythemselves in an interlocking plastic manner into the inner wall of thebearing housing 63. Preferably, the cutting edges are inclined againstthe axis G such that the fastening means 951 have a barb-likeembodiment. As a result, the securing rings 95 can be moved axially onlyin the direction against the gear wheel 7 in the bearing housing 63. Asa result of the preloading force F that acts in the assembled state, thesecuring rings 95 are loaded oppositely, as a result of which thefastening means 951 cling to the inner wall of the bearing housing 63 asa result of their barb-like embodiment. Expressed differently, thesecuring rings 95 have a self-affixing embodiment.

An axial preloading force F is applied during the assembly of therolling-element bearing arrangement 9 for the purposes of avoidingbearing play in the direction of the axis G. It is applied by thesecuring rings 95, the spring elements 94 embodied as preloadingelements and the ball bearings 91 on the bearing faces 81 of the bearingrings 8 on the bearing rings 8, as indicated by force arrows in FIG. 4.The preloading force F is maintained during the entire service life bythe elastic spring elements 94 that act as preloading elements. As aresult, the two bearing rings 8 are pressed against one another axially,wherein the force F acting on the bearing faces 81 during operation istransmitted completely in the power flow through the bearing rings 8.What is advantageous here, in particular, is that the plastics materialof the core element 71 is not situated in the power flow between thebearing rings 8, i.e., it is not subjected to pressure. This unloadingensures that the plastics material is not plastically deformed byflowing.

FIG. 5 shows the individual parts of the gear wheel 7 and of therolling-element bearing arrangement 9 pulled apart in an explodedillustration in the direction of the axis G.

FIG. 6 shows an adjustment drive 6 during setting in a setting device,which comprises an axially movable compression column 96 and a counterbearing 97 that is stationary relative thereto. By means of a source offorce (not illustrated here), the compression column 96 can have applieda preloading force F thereto, the latter consequently serving aspressing-in force.

In order to set the rolling-element bearing arrangements 9, the onesecuring element 95, which lies to the left in FIG. 6, is axiallysupported at the counter bearing 97 while the other securing ring 95,situated at the right in the drawing, is pressed against the gear wheel7 in the axial direction with the preloading force F by way of thecompression column 96. Here, the securing ring 95 is initially displacedas far as against the spring element 94 by way of the above-describedbarb-shaped embodiment of the fastening means 951. Upon contact, thespring element 94 is axially compressed by the preloading force F andthe preloading force F is introduced into the rolling-element bearingarrangement.

The magnitude of the preloading force F with which the gear wheel 7 ispreloaded in the rolling-element bearing arrangement 9 can be effecteddepending on a breakaway torque M that has to be applied to turn thegear wheel 7. To this end, the gear wheel 7 is driven to rotate, forexample by the servomotor 66 of the drive unit. Alternatively, as perFIG. 3, 4, 6, 7 or 8, in the case of a rotational spindle drive, inwhich the threaded spindle 62 is connected to the gear wheel 7 forrotation therewith, the drive can be brought about by an externaladjustment drive (not illustrated here), which drives the threadedspindle 62 to rotate.

The breakaway torque M can be measured by means of suitable sensors, forexample by way of torque sensors, or by way of a motor current of theservomotor 65 or an external adjustment drive.

During the rotating drive, the axial preloading force F is applied bythe compression column 96 on the bearing arrangement proceeding from apredetermined start value and said preloading force is increasedcontinuously or step-by-step and preferably measured by means ofsuitable force sensors in the process. As a result, there is an increasein the bearing friction, and the measured breakaway torque M, whichcorrelates to the preloading force F, likewise increases.

The measured breakaway torque M is compared, preferably automatically,to a predetermined torque target value.

If the measured breakaway torque M is less than the predetermined torquetarget value, this means that the bearing play is still too large, orthe preload is still too small, and so the required rigidity of thebearing arrangement and play-free running under load conditions duringoperation are not yet ensured. In this case, the preloading force F isincreased, and the measured breakaway torque M is measured again andcompared to the torque target value.

The aforementioned steps are run through until the measured breakawaytorque M as bearing state variable attains the predetermined torquetarget value as state target value. In the axial position attained inthe process, in the preloading position, the securing ring 95 and hencethe spring element 94 are affixed relative to the bearing housing 63.The axial affixment can be effected by virtue of the barb-shapedfastening means 951 being buried in the inner wall of the bearinghousing 63 in an interlocking plastic manner as a result of thepreloading force F exerted by the spring element 94 and then securingthis in the preloaded position during unloading or retraction of thecompression column 96. As an alternative or in addition thereto, anaffixment can be brought about by substance-to-substance bonding, forexample welding or the like, or by means of additionally insertedfastening means.

As an alternative or in addition thereto, the preload can be setdepending on the bending stiffness of the adjustment drive 6. To thisend, the bearing arrangement is subjected to bending by a tilt moment K,which is introduced transversely into the threaded spindle 62. Theradial deflection x occurring in the process, which is measured by meansof a path measuring device 99, is a measure for the stiffness. It isdependent on the preloading force F, with a high preloading force Fcorrelating with a low deflection x and, accordingly, a high stiffness

The deflection x, which serves as a correlating bearing state variable,corresponds to a displacement of the gear wheel 7, for example a tilt inthe bearing housing 63, which is produced by the tilt moment that servesas load moment. The measured deflection x is compared to a referencevalue of a maximum admissible displacement that is assigned to astiffness threshold corresponding to the state target value.

The required stiffness is not provided for as long as the measureddeflection x is greater than a predetermined stiffness threshold. Inthis case, the preloading force F is increased until the measureddeflection x is less than or equal to the stiffness threshold withinpredetermined tolerance ranges.

Setting the preload can be effected by regulating the breakaway torque Mor the tilt moment K, or else by taking account of both load moments Mand K.

Alternatively, the preload can be set by regulating the applied andmeasured preloading force; if the latter attains a predeterminedthreshold, the so-called target preloading force, the preloading elementis affixed and setting the preloading force is completed.

FIG. 7 shows a second embodiment in which the outer bearing ring 93lying to the left in the drawing is axially supported against an axialcounter bearing 67 that is formed by a moulding of the bearing housing63 embodied as a shoulder, instead of the one securing ring 95.Moreover, this embodiment has only one spring element 94, which isembodied as an O-ring made of rubber-elastic material, said springelement being arranged to the right in the drawing between the outerbearing ring 93 and the securing ring 95.

FIG. 8 shows a third embodiment which has two securing rings 95, likethe embodiment as per FIG. 6, but only one spring element 94, which isembodied as an O-ring or similar elastic element, like in FIG. 7.

In respect of the bearing of the gearwheel 7, the fourth embodiment asper FIG. 9 has a similar design, in principle, as the embodimentpresented in FIGS. 4 and 6. However, in contrast thereto, this is aplunger spindle drive, in which the threaded spindle 62 engages in athread in the spindle nut 61 that is connected to the gearwheel 7, i.e.,it is not connected to the gearwheel 7 for rotation therewith.

The fifth embodiment as per FIG. 10 is distinguished by virtue of atleast one of the securing rings 95, or else both securing rings 95,inherently having an axial spring-elastic embodiment. As it were, thepreloading element according to the invention has an integratedembodiment in at least one securing ring 95.

The embodiments shown in FIGS. 7, 8, 9 and 10 can be set as described inrelation to FIG. 6.

1.-17. (canceled)
 18. An adjustment drive for a steering column that isadjustable by motor for a motor vehicle, comprising: a spindle nut, athreaded spindle with an axis, said threaded spindle engaging in thespindle nut, a drive unit, and a gear wheel connected to the spindle nutor the threaded spindle for rotation therewith, the gear wheelconfigured to be rotated about the axis by the drive unit and which isrotatably mounted about the axis in a bearing housing in a bearingarrangement between two outer bearing rings that are axially supportedat the bearing housing, wherein the outer bearing rings each have, ontheir sides facing one another, a circumferential outer bearing facethat is coaxial to the axis, each said outer bearing face positionedopposite a bearing face formed on the end side at the gear wheel,wherein at least one of the outer bearing rings is supported in anaxially resilient manner at the bearing housing by way of an elasticpreloading element configured to exert a preloading force that axiallybiases the two outer bearing rings against one another.
 19. Theadjustment drive of claim 18 wherein the preloading element comprises aring-shaped spring element.
 20. The adjustment drive of claim 18 whereinthe preloading element is supported at a securing element that isconnected to the bearing housing.
 21. The adjustment drive of claim 18wherein the preloading element comprises a securing element.
 22. Theadjustment drive of claim 21 wherein the securing element comprisesfastening means for affixment inside the receiving space.
 23. Theadjustment drive of claim 18 wherein the preloading element is anintegral securing element.
 24. The adjustment drive of claim 18comprising rolling bodies positioned between the gear wheel and theouter bearing rings.
 25. The adjustment drive of claim 18 wherein one ofthe outer bearing rings is supported at the bearing housing at a counterbearing in an axially rigid manner.
 26. The adjustment drive of claim 18wherein the bearing housing comprises a hollow cylindrical receivingspace in which the outer bearing rings and the gear wheel are arrangedcoaxially in relation to the axis.
 27. A steering column that isadjustable by motor for a motor vehicle, comprising a carrying unitconfigured to attach to a vehicle body, an actuating unit held by thecarrying unit, a steering spindle rotatably mounted about a longitudinalaxis in the carrying unit, and an adjustment drive connected to thecarrying unit and to the actuating unit, via which the actuating unit isadjustable relative to the carrying unit, wherein the adjustment drivecomprises: a spindle nut, a threaded spindle with an axis, said threadedspindle engaging in the spindle nut, a drive unit, and a gear wheelconnected to the spindle nut or the threaded spindle for rotationtherewith, the gear wheel configured to be rotated about the axis by thedrive unit and which is rotatably mounted about the axis in a bearinghousing in a bearing arrangement between two outer bearing rings thatare axially supported at the bearing housing, wherein the outer bearingrings each have, on their sides facing one another, a circumferentialouter bearing face that is coaxial to the axis, each said outer bearingface positioned opposite a bearing face formed on the end side at thegear wheel, wherein at least one of the outer bearing rings is supportedin an axially resilient manner at the bearing housing by way of anelastic preloading element configured to exert a preloading force thataxially biases the two outer bearing rings against one another.
 28. Amethod for setting a bearing arrangement of an adjustment drive for asteering column that is adjustable by motor for a motor vehicle,comprising a threaded spindle with an axis, said threaded spindleengaging in a spindle nut, and a gear wheel which is connected to thespindle nut or the threaded spindle for rotation therewith and which isrotatably mounted about the axis in a bearing housing in a bearingarrangement between two outer bearing rings that are axially supportedat the bearing housing, wherein an outer bearing ring is supported in anaxially resilient manner at the bearing housing by way of an elasticpreloading element, the method comprising: applying an axial preloadingforce to the preloading element, applying a load moment to the gearwheel and measuring the load moment, measuring a bearing state variablethat is correlated with the load moment, comparing the measured bearingstate variable with a predetermined state target value, when themeasured bearing state variable deviates from the state target value:modifying the axial preloading force, and when the measured bearingstate variable attains the state target value: affixing the preloadingelement in an axial preloading position at the bearing housing andcompleting the setting process.
 29. The method of claim 28, furthercomprising: applying a breakaway torque as load moment for rotationaldriving of the gear wheel and measuring the breakaway torque in theprocess as a correlating bearing state variable, comparing the measuredbreakaway torque as a bearing state variable with a predetermined torquetarget value as a state target value, when the measured breakaway torqueas a bearing state variable is smaller than the predetermined torquetarget value as a state target value: increasing the axial preloadingforce, and when the breakaway torque as a bearing state variable attainsthe predetermined torque target value as a state target value: affixingthe preloading element in an axial preloading position at the bearinghousing and completing the setting process.
 30. The method of claim 28,further comprising: applying a tilting moment as a load moment acrossthe axis on the gear wheel and measuring a displacement of the gearwheel relative to the bearing housing in the process as a correlatingbearing state variable, comparing the measured displacement as a bearingstate variable with a predetermined stiffness threshold as a statetarget value, when the measured displacement as a bearing state variableis greater than the predetermined stiffness threshold as a state targetvalue: increasing the axial preloading force, and when the measureddisplacement as a bearing state variable attains the predeterminedstiffness threshold as a state target value: affixing the preloadingelement in an axial preloading position at the bearing housing andcompleting the setting process.
 31. The method of claim 28 wherein thepreloading force is measured when the preloading force is applied. 32.The method of claim 28 wherein the preloading force is exerted on asecuring element that is arranged in front of an outer bearing ring. 33.The method of claim 32 wherein the securing element is movable relativeto the bearing housing in the direction of the preloading force andembodied to affix itself at the bearing housing against the preloadingforce.
 34. A method for setting a bearing arrangement of an adjustmentdrive for a steering column that is adjustable by motor for a motorvehicle, comprising a threaded spindle with an axis, said threadedspindle engaging in a spindle nut, and a gear wheel which is connectedto the spindle nut or the threaded spindle for rotation therewith andwhich is rotatably mounted about the axis in a bearing housing in abearing arrangement between two outer bearing rings that are axiallysupported at the bearing housing, wherein an outer bearing ring issupported in an axially resilient manner at the bearing housing by wayof an elastic preloading element, comprising the steps of: applying anaxial preloading force to the preloading element, measuring the axialpreloading force, comparing the measured preloading force with apredetermined target preloading force, when the measured preloadingforce deviates from the predetermined target preloading force: modifyingthe axial preloading force, and when the measured preloading forceattains the predetermined target preloading force: affixing thepreloading element in an axial preloading position at the bearinghousing and completing the setting process.